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79 datsun 620 automatic


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#1 rootbailey

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Posted 25 April 2018 - 05:42 PM

I was wondering would a 71 datsun pickup 4 speed transmission fit a 79 datsun620 king kab

#2 rootbailey

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Posted 25 April 2018 - 05:48 PM

Will a 71 datsun pickup transmission fit a 79 620 king kab

#3 kelowg

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Posted 25 April 2018 - 06:56 PM

Fit,well can be made to fit but 79 is long trans and 71 is way shorter and bit weaker



#4 datzenmike

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Posted 25 April 2018 - 06:56 PM

Not without some work. The 521 had a 26" long transmission. The '79 uses a 31.5" long transmission and its stronger for a two liter engine in a truck.

 

 

 

 

Now I see the '79 is an automatic. Same length also at 31.5". If converting to a standard get a 4 or 5 speed from a 260 or 280z, '74 and up 620, 810 or maxima to '84, 1980 2wd 720 truck or a '79 and up 280zx. (non turbo) It will drop right into a '79 for length.


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#5 rootbailey

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Posted 26 April 2018 - 09:37 AM

Will my automatic drive shaft fit the 4 speed transmission

#6 Crashtd420

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Posted 26 April 2018 - 10:25 AM

Don't forget about the fact you'll need a clutch and flywheel instead of the torque converter....
And then the obvious the pedals and a clutch master....

#7 datzenmike

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Posted 26 April 2018 - 11:17 AM

'79 620 automatic......... 31.5" long

'79 4 or 5 speed............ 31.5" long

521 4 speed.................. 26" long

 

 

To convert the automatic to a standard you will need...

 

A set of clutch and brake pedals for a 620.

A 620 clutch master cylinder complete with the pushrod connecting it to the clutch pedal.

A hydraulic hard line and connecting flex hose to the slave cylinder

A truck slave cylinder with push rod to connect to the transmission clutch arm*.

A clutch arm and dust boot*

Shift lever and dust boot*

A 6 bolt L series flywheel and mounting bolts

New clutch and pressure plate matched to the flywheel clutch diameter.... either 200mm or 225mm

A release bearing holder or collar properly sized to match your choice of 200 0r 225mm clutch1

A release bearing1

A pilot bushing for the end of the crankshaft.

 

* may come with the transmission

1 may come with the clutch kit


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#8 datsunaholic

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Posted 26 April 2018 - 12:30 PM

Will my automatic drive shaft fit the 4 speed transmission

Not the 521 one. 


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#9 Bleach

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Posted 26 April 2018 - 12:35 PM

If you are after a manual transmission for your 1979 truck and are unable to find Datsun truck parts in your area, remember there are other sources to replace your transmission.

 

Other Datsuns used the L-series engine so maybe there is a 280Z or 280ZX with a 5-speed. Other rare cars like the Datsun 810 or Maxima (before 1985 only) if they are manual.

The z-car would work from 1975-83. Even the 240SX 5-speed from the early 1990's will work if you switch out the bellhousing with a Datsun bellhousing. I'm not sure what the details are on the 240SX swap but you could look that up.


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#10 rootbailey

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Posted 26 April 2018 - 07:36 PM

Thanks for all the help guys the reason for changing is this automatic is geared super low at 45mph it sounds like it is turning like 5000 rpm's

#11 flatcat19

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Posted 26 April 2018 - 07:51 PM

Too bad you are so far away. I'm parting out an entire manual trans 620 with a 5 speed.

You can't hang if your nuts haven't dropped...it's physics


#12 datzenmike

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Posted 26 April 2018 - 08:00 PM

Thanks for all the help guys the reason for changing is this automatic is geared super low at 45mph it sounds like it is turning like 5000 rpm's

 

The automatic is geared perfectly for the engine and truck weight. 'Sounds like' and what it is doing are very open to interpretation without a tach.  A 23.65" diameter tire with a 4.375 differential and an automatic in third would be going 80.44 MPH at 5,000 RPM.

 

 

I bet the clutch fan has seized. With the engine off grab the plastic fan blades and try to turn them. If stuck,the bearing has seized and the clutch is not slipping to keep the fan speed at 2,200 RPMs. When this happens it sounds like an F-18 taking off.


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#13 Bleach

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Posted 27 April 2018 - 08:09 AM

Your top gear in the auto is basically the same as 4th gear in a manual. I bet you're going to want to wait to find a true 5-speed manual. You'll also have a bit more power with the manual transmission.

 

Look for a Datsun truck 5-speed (1977-80) or Z-car transmission (1975-83) Those are all long tail and made for the L-series engine. Be sure to get the flywheel off of the L20b or L28 when you get the transmission. (if possible) then buy a new clutch kit for whatever vehicle you pulled it from.

 

Keep in mind there are a couple different sizes of clutch kits. Mainly 220mm surface or 240mm surface (only found on some z-cars)

 

Also you might consider buying an aftermarket tachometer. You can get small ones for $30-40 and install it in the left gauge pod or above or below the dash just for a reference.


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#14 rootbailey

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Posted 27 April 2018 - 05:00 PM

I'm going to buy a tach for it. The fan does sound like it is flying away and it goes from 1st gear to high gear its like 2nd gear is not there any thoughts on that

#15 datzenmike

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Posted 27 April 2018 - 05:52 PM

Well my 710 sedan seemed like that too. What was happening was it was up shifting so soon that I mistook 2nd for first and only felt the one shift. (into 3rd) If I floored it from a start it would stay in first long enough to really feel the 1-2 shift and then the 2-3. They were there all right.

 

 

My FSM suggests that the highest speed in second before it shifts to 3rd is about 65 MPH. If you can go 70 or more on the highway, I would say that it's definitely in 3rd.

 

The delay of the 2 to 3 shift can be causes by the vacuum line from the intake having a leak or being loose. The transmission modulator valve will think wrongly that the low vacuum is a sign that the throttle is wide open. It will probably delay the 1-2 shift to about 40 MPH as well.

 

 

Check the clutch fan for stiffness. It normally will firmly but smoothly resist turning with finger pressure. You cannot spin it, but it will turn like it's in thick honey. The stiffer it is the faster it will spin. If seized it will turn very fast and make a roaring sound. I've held a good clutch fan and started the engine. You can easily enough hold it still while the engine idles. I do NOT recommend trying this but it shows how much slip there is. 


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#16 rootbailey

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Posted 28 April 2018 - 05:47 AM

Ok well I found a 4 speed and a five speed but the 5 speed is off an 84 pickup will it fit my truck?

#17 datzenmike

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Posted 28 April 2018 - 05:56 AM

Nope.

 

The '84 is either a Z series or a diesel engine and you have an L series engine. They sit in the engine compartment with different amounts of lean. The Z series will bolt to the L series but when installed it will twist the transmission to the right and the shifter will be in the passenger's hip. If the 4 speed is a 71B you can take the front case off, (the part with the L series bolt pattern and tilt) and put it on the Z series 5 speed and convert it for proper use on an L20B. 

 

The other consideration is the transmission length. 720s had 26" and 31.5" lengths. You would want a 31.5" for your 620.


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#18 rootbailey

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Posted 29 April 2018 - 05:57 AM

I bought another whole truck lol its a 79 620 king cab 4 speed the truck is rough but the engine and transmission is good got the whole thing for $200 bucks so I'm just gonna switch change it over to the 4 speed thanks for all your help

#19 datzenmike

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Posted 29 April 2018 - 06:14 AM

Nice!! That is the most perfect way to do it but seldom available. Everything you need is there. Too bad it's a 4 and not a 5 speed but... You'll have to decide if the clutch has enough wear left on it to keep. The release bearing... for $10 definitely change. You need a $3 pilot bushing for the end of the crankshaft (just lightly hammer in with block of wood) and I would change the $5 oil seal in the drive shaft end of the transmission, they just pry out with a screwdriver and hammer in. Definitely drain the oil before removing the trans. When ready refill with new GL4 80/90w.

 

 

The automatic and the standards use different differential gear ratios so your speedometer will be out, reading lower than actual speed. Keep your eyes open for the RED 20 tooth speedometer pinion sleeve from an earlier standard truck. The automatic sleeve will not fit the standards.


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#20 rootbailey

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Posted 29 April 2018 - 07:19 AM

Ok thanks you have been a great help and ill keep you posted